What are lipids & Classification of lipids

Fats (or lipids) are fatty acid Ester of alcohols and related substance, which are insoluble in water but get dissolved in a number of non- polar organic solvent such as benzene, Ether, Acetone, chloroform etc.
There are three types of lipids
 1:-simple lipids
2:- compound lipids
3:-derived lipids

Simple lipids:- simple lipids are the Ester of fatty acids and alcohols which no additional groups,such as true fats, waxes, cutin and suberin.

Compound lipids:- compound lipids or fats have additional group beside fatty acid and alcohol,such as phospholipids, glyco-lipids and sulpho-lipids etc.
True fats:- They are triglycerides which are formed by esterification of 3 molecule of fatty acid which one molecule of trihydric alcohol glycerol.
·The three fatty acids may be similar (example:- Tripalmitin) or disimilar (example:- butter).
· Where R-CO- is derived from the fatty acid at each esterification a molecule of water is given out.
· If a true fat is hydrolysed, Ester linkage breakdown and the two components of the fat are regenerated.
· Hydrolysis by mean of alkalis is called 'Saponification' as it yield salts of fatty acid or soaps.
·  The soap action of the fatty acid is due to the presence of extremely polar water soluble end of an otherwise extremely non-polar water insoluble substance.
· True fats  chiefly serve as reserve food. they are stored in the cell inside sphaerosomes or oil bodies.
Waxes
1:- Wax is a soft hydrophobic mixture of long chain carbon compound including alcoholic Ester of fatty acid which are poor in oxygen and having a melting point between 36 to 200 degree Celsius.
2:- Waxes differ from true facts in having fatty acid ester of long chain monohydric alcohols Free alcohol, free hydroxy fatty acid, sterols and other fat-like substance may also occur in waxes.
3:- Waxes found on the the upper surface of floating leaves prevent wetting and submergence of the leaves. wax found on the surface of aerial part in useful in reducing insulation and transcription.
Cutin
1:-It is a complex produced by cross- esterification and polymerization of hydroxy fatty acid and having simple fatty acid with or without esterification by alcohols other than glycerol.
2:- It occur in the aerial epidermal cell walls and as a separate layer of a cutin on the outside of this epidermal cells.cutin reduce the rate of a transpiration and binds epidermal cell.
Suberin
It is a mixture of a fatty material having condensation product of a glycerol and phellonic acid or its related substance.suberin makes the cell wall strong and impermeable. it occur in the Wall of cork and endodrmal cells.
Compound lipids
Phospholipids
They are the triglycerides where on fatty acid is replaced by phosphoric acid linked to choline (in lecithin), ethanolamine (in cephalin) or inositol(in ionoside) etc
Glycolipids
They are those fats and lipids in which the terminal hydroxyl group of a glycerol is attached to a sugar instead of fatty acids. they occur especially in the chloroplast membranes.

Derived lipids
Steroids and sterols
The complex lipids which are unsponifiable include the biochemically important class, the steroids they fall in the category of isoprenoid lipids along with carotenes & bile acids.
· They are the tetracyclic Crystalisable alcohols of high molecular weight example:- cholestrol, cortisone, testosterone, ergasterol.
 · Cholesterol is important metabolically in human beings and plants where it occur.

Cholesterol

Function of lipids & fats
1:-They serve as food reserve in both plants and animals. their oxidation yield energy for growth.
2:- They function as a concentrated food because as compared to carbohydrates they yield more than twice as much energy per unit weight.
3:- In seeds and spores, they help in a thermal insulation protection from ultraviolet radiation.
4:- vitamin A, D, E and K are soluble in fats. therefore the functions as the transportable energy supply.
5:- In animals fat from an insulating layer below the skin for protection against low temperature.
6:- Several plants fats are edible. so are animals fats present in milk.
7:-  Soap is a manufactured from plant fats.(previously from animal fat).
8:- Steroids act as hormones example:- Testosterone.

Bonding in solids

Every atoms are held together in said by interatomic force. These forces actong between the atom are electrostatic in nature. The process of holding atom together in a crystal is known as bonding.
Types of bonding in solids on the basis of electron distribution or forces.

1.ionic bond:- These bond are formed in crystal in which electron are transferred from one atom to another atom. Such that the crystal is made up of positive ion or negative ion. It is non-directional in nature. Its bonding energy is of order of 5ev to 10ev.
Example:- Nacl, CaO etc.
Properties of ionic bonds
1. They have higher enthalpies of fusion and vaporization than molecular compounds.
2.They are hard.
3.They are brittle.
4.They have high melting points and also high boiling points.
5.They conduct electricity but only when they are dissolved in water.

2. Covalent bond:- These bond in crystal are formed by sharing of electron equally between neighbouring atom. It is directional in nature. Its crystal are brittle and hard. It is less strong than ionic bond. Example:-chlorine, diamond etc.
Properties of covalent bond
1.-Low boiling points and melting points.
2. Various colors.
3. Poor conductors of heat and electricity.
4.Brittle solids.

3. Metallic bond:- In crystal with these bond. The valence electrons of constituent atom free to move through out the crystal. They do not form the permanent bond Example:- copper,silvar etc.
Properties of metallic bond.
1.Malleability.
2.Ductility.
3.High melting and boiling point.
4.High electrical and thermal conductivity.
5.Metallic lustre.

4. Vandar waal bond:- In this bond crystal arises due to dipolar force between atom of the crystal. its a weak binding. With low melting and boiling point.
Example:- Argon, neon etc.
Properties of Vandar waal bond.
1. These bonds are weak force of attraction.
2. Low melting and boiling point.
3. Low electrical and thermal conductivity.
4.  This bond break easily.
5. Metallic lustre

5.Hydrogen bond:- The hydrogen bond is formed between an atom of hydrogen and extremely electronegtive atom.Example:- fluorine, oxygen, nitrogen etc. It is essentially ionic in chracter. Example:- Hydrogen water and ice.
Properties of hydrogen bond.
Solubility: Lower alcohols are soluble in water because of the hydrogen bonding which can take place between water and alcohol molecule.
Volatility: As the compounds involving hydrogen bonding between different molecules have a higher boiling point, so they are less volatile.
Viscosity and surface tension: The substances which contain hydrogen bonding exists as an associated molecule. So their flow becomes comparatively difficult. They have higher viscosity and high surface tension.
The lower density of ice than water: In the case of solid ice, the hydrogen bonding gives rise to a cage-like structure of water molecules. As a matter of fact, each water molecule is linked tetrahedral to four water molecules. The molecules are not as closely packed as they are in a liquid state. When ice melts, this case like structure collapses and the molecules come closer to each other. Thus for the same mass of water, the volume decreases and density increases. Therefore, ice has a lower density than water at 273 K. That is why ice floats.

HYDROGEN BONDING